Hey Bill,
I've had no real experience with hand styles although I have had it demonstrated to me AND I sat on the loud side of Simon O'Dwyer for several sessions - if that's experience then yeah :)
Roscommon is the most common and is where the right (striking) hand is turned with the fingers toward the body, a bit like an extension of the 'kerry' bodhran technique. The flats of the backs of the fingers strike the drum.
I've seen it too (Tommy Hayes) where the thumb and pinky knuckles are extended and played like a
Tipper.
It's very rare and I've never really seen it played as a primary style apart fromn Simon and his Charlie Byrne monster Jennett drum. It didn't strke me as being a tonal style, more about attack; the head was like a brick. I expect the style developed from convenience although there are great players out there.
Playing with finger tips is a different matter altogether - That I love!
HTH
Paul